If you had to do this only once, wouldn't simple, low-level, brute force be the easiest way? There are at least a half-dozen ways to list all the computers on a network. Dump that into a text file. Run a quick search/replace in your favorite text editor to add in your net command and - POOF - you've got a batch file you can run once and be done. The whole thing would probably take less than 5 minutes to generate and execute.

Sure, if you knew the powershell command (which you didn't), you could do it in a more sophisticated way. But quick and dirty works every time.